The present invention relates to an electrostatic image-developing toner and a developer containing the same, used for developing electrostatic latent images formed in electrophotography method, electrostatic recording method, etc. More particularly, the present invention relates to a positively charged electrostatic image-developing toner and a negatively charged electrostatic image-developing toner, both of which contain specific materials.
The developer used for electrocopiers, etc. is once deposited on an image carrier such as a photoreceptor on which an electrostatic image has been formed, in the developing step, then the deposited developer is transferred from the photoreceptor to a transfer sheet in the transfer step, and the transferred developer is finally fixed on a copying paper in the fixing step. As the developer used for developing the electrostatic image formed on a latent image carrier, there are known two-component developer comprising a carrier and a toner, and one-component developer (magnetic toner and non-magnetic toner) which requires no carrier.
As a toner contained in the said developer, there can be mentioned a positively charged toner and a negatively charged toner. As the agents for imparting charge to the positively charged toner, there have been known the charge-imparting or controlling agents which are added to the toner, such as Nigrosine dyes and quaternary ammonium salts, and the coating agents which can impart desired charge to the carrier. On the other hand, as the agents for imparting negative charge, there have been known the charge-imparting agents such as metallized azo dyes, a fine inorganic powder, a fine organic powder and carrier-coating agents.
However, any of these conventional charge-imparting agents was not always satisfactory in their charge-imparting effect, and it has been difficult to obtain a toner which shows proper charging property stably without being affected by the environmental factors and also exhibits a favorable change of charge with the passage of time. Especially, the toner containing the conventional charge-imparting agent mentioned above has the problem that it causes an image blotting due to increase of a background (BKG) level in continuous copying operation under a high temperature and high humidity condition, making it unable to obtain a stabilized copy density.
The toner in the electrostatic image developer is stirred in use and as a result, the toner is frictionally charged through contact with carrier or charging medium such as charging blade. In this process, in the case of the positively charged toner, a binder resin as a main component of the toner, except for certain types of resin, has a strong tendency to get negatively charged, so that it is hard to obtain a positively charged toner which exhibits always constant and sufficient charging performance. At starting the use of developer or at re-starting the use of the developer after allowing to stand for long-time, the build-up of charge at the start of stirring of the developer is bad, and electrostatic attraction between the toner and the said charging medium becomes insufficient, thereby causing scatter of the toner in the apparatus. Such phenomenon of toner scattering due to slow the build-up of charge of toner becomes conspicuous especially under a high temperature and/or high humidity condition.
In the case of the negatively charged toner having negative polarity of charge against the carrier, the toner components adhere to the carrier particle surfaces, thereby reducing the charge-imparting effect of the carrier, so that the amount of charge on the toner particles decreases gradually as the copying operation is repeated, and finally the toner particles become positively charged. Since the toner particles are not attracted strongly to the electrostatic latent image, the toner particles may deposit on other part than the latent image on the photoreceptor to cause staining of the image. Also, some of the toner particles may be scattered from the photoreceptor into the copying machine.
For solving these problems, there has been proposed a developing toner prepared by adding a basic magnesium aluminum hydroxycarbonate hydrate powder which is composed of a compound analogous to that of the present invention, to the toner particles (Japanese Patent Application Laid-Open (Kokai) Nos. 7949/91, 27050/91 and 103866/91).
A developing toner has been also proposed in which, in order to enhance an ozone resistance of the photoreceptor, a hydrotalcite compound which is analogous to the compound of the present invention, is added to the toner particles (Japanese Patent Application Laid-Open (Kokai) No. 166461/90).
These proposed developing toners, however, have the problem of environment dependency of image density, that is, a phenomenon that the image density is lowered under a low temperature and low humidity condition, which makes it hard to obtain a stabilized image density.
As a result of strenuous studies for overcoming these problems, it has been found that by adding a compound represented by the following formula (I) to the toner particles, the obtained electrostatic image-developing toner shows a good charging property and little environment dependency of image density. EQU M.sup.1 y.sub.1.M.sup.2 y.sub.2.M.sup.3 x.(OH).sub.2.Ax/n.mH.sub.2 O(I)
(wherein M.sup.1 is at least one of the divalent metals selected from the group consisting of Mg, Ca, Sr and Ba; M.sup.2 is at least one of the divalent metals selected from the group consisting of Zn, Cd, Pb and Sn; M.sup.3 is a trivalent metal; A is an anion of n valency; n is integer of 1 to 4; and x, y.sub.1, y.sub.2 and m are the positive numbers satisfying the relations of 0&lt;x.ltoreq.0.5, y.sub.1 +y.sub.2 =1-x and 0.ltoreq.m&lt;2).
The present invention has been attained on the basis of such finding.